Stitching photos with 123D Catch

Stitching is the correlation of the photos you took of your object. It aligns the photos to each other to make a proper sequence. Sometimes, the Autodesk server will have a difficult time choosing the proper photo for stitching; it will either discard the photo from the sequence or choose the wrong placement of a photo. These problems can be fixed by manually stitching the photos. In this recipe, we'll learn how to do this.

Getting ready

Hopefully, you don't have any stitching problems with the four objects you scanned, but we will need a photo sequence with stitching problems for this recipe. There's an easy way to illustrate the repair of unstitched photos, even with a good processed scan. Choose one of your Photo Scene data files for the following recipe, and make a copy of the folder and all of its contents. Use the copy for this recipe.

How to do it...

Open 123D Catch and sign in. Open an existing capture and proceed as follows:

1. Choose a photo from the thumbnail strip at the bottom. Right-click on it, and choose Unstitch Photo from the pop up. As shown in the following screenshot, the thumbnail darkens with an embedded yellow warning symbol:
   
2. The photo sequence now has an unstitched photo. To repair it, double-click on the darkened photo. A new window opens, as shown in the following screenshot:
   
3. At the bottom-left side, the Manual Stitch window outlines the basic procedure in three steps. Review these steps before continuing.
4. The first step is to choose the best photos to align. 123D Catch chose two photos, and they are displayed on the right-hand side of the window. We can keep these or change them by scrolling through the thumbnails by clicking on the arrows.
5. For the second step, we need to choose a point on the unstitched photo that correlates with the same exact point on the other two photos. Left- click and hold on the point. A magnifier opens, giving us a better definition of the immediate area. This is illustrated in the following screenshot:
   
6. Release the mouse when you determine your point. A yellow marker appears. If you're not happy with your choice, right-click on the yellow marker and choose Delete Point in Image from the pop up.
7. On the photo in the top-right corner of the window, repeat the selection for the proper correlation point. When the point is accepted, a suggested point will be automatically made on the third photo in the bottom-right corner. Instead of a circle registration point, it will be a square. Left-click on it and hold to determine if it's correct. If it is, release the mouse. When all the points are accepted, they will turn green.
8. For the third step, repeat the first and second steps until all the four matched points are made. Your project should look similar to the following screenshot:
   
9. When all the four points are matched, a pop up will appear and prompt you to update your scene. Choose Submit. Another pop up will appear and prompt you with a Continue option. The processing must take place at the Autodesk server. This requires the upload of the changes and a wait time. When the processing of the scene is finished, a new file will be returned.

How it works...

For our recipe, we intentionally unstitched a photo from our sequence. This gave us a situation to repair it using manual stitching. Sometimes, we may find that it's important to unstitch a photo that has been incorrectly processed by the Autodesk server. This can occur when similar sides, such as the sides of a cube, are confused in the interpolation of the scene and an erratic camera track is produced. Sometimes, unstitching a photo out of sequence and restitching it where it belongs will solve the problem.

There are situations when the incorrect exposure or focus of an image is undesirable. This can be the case when the output is for export as an animation. By unstitching the problematic photo, the result will be better.